40 milliseconds (one frame) delay is about as much as is acceptable for live radio camera links
“perform really well in a controlled environment,” admits Valentino. But you don’t have control over the parameters of these chipsets, so “you have no flexibility.” However, some manufacturers are now developing MIMO for broadcast bands (7, 10 and 12GHz). MIMO could, theoretically, run 100Mbps through 10MHz of bandwidth, whereas the maximum at present with MPEG-4 would be about 20- 25Mbps, allowing four radio cameras in the same bandwidth or a single camera at higher quality. “This opens the door to using JPEG2000 at 80Mbps, which is indistinguishable from a live camera — and you’d get two or three milliseconds delay, which is going to be a big game changer,” says Valentino. Another technology that should benefit wireless cameras, eventually, is H.265, which should be about 30-40% more efficient than H.264, and about 70% more efficient than MPEG-2. However it will take some time to optimise H.265 for wireless cameras. H.264 is only really becoming optimal now. MPEG-2 is still the main
compression system for broadcast wireless systems. Typically, a stable link with good pictures would require about 18Mbps, says Valentino. BSI does use some H.264 4:2:0 (generally 8-bit) links for in-car point-of-view cameras, which he says works well for those types of applications. “It is too low for high quality, but if it could go to 15-20Mbps MPEG4 at 4:2:2 the quality will outperform MPEG-2.”
Without delay Valentino believes that 40 milliseconds (one frame) delay is about as much as is acceptable for radio camera links for live use. “You can only get away with greater delay if the camera is away from other live cameras. Generally, in music and sports, where radio microphones are involved, 40 milliseconds is as much as we can tolerate.” Although the Boxx Meridian
transmitter has about one millisecond delay, in reality the signal has to be retimed, making it one frame, to genlock to the OB truck. For Walker “the real issue you see with lip sync is when they put people on a big LED screen on the show, so they are already out of sync. If we were the only people adding delay, it wouldn’t be a problem, but every department seems to add a delay.” For The X Factor there was a huge screen in the background
showing, for example, one of the judges talking while another camera caught the contestant’s reaction. The image on the display had a seven frame delay and was “just on the edge of acceptability when seen from a wired camera,”
so a wireless camera wouldn’t be used for that type of shot. The Boxx system also has a full
return feed, which can carry prompter information, so the presenter can use the mobile camera. This has an added
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benefit. “It gives redundancy on location, as you can reverse the link to transmit,” explains Walker. While some live shows use
wireless cameras to give them greater creative freedom, others use them for safety reasons. For
Example, Boxx recently worked on a pilot show with CTV called Celebrity Splash, where celebrities were being taught to dive: this required three wireless cameras for poolside shots because cables would have been dangerous.